1. Field of the Invention
The present invention relates to a variable-delivery vane-type rotary compressor, particularly to a rotary compressor which is used as a refrigerant compressor for an air conditioner for a vehicle or the like.
2. Description of the Prior Art
Generally, in order to control discharge in a vane-type rotary compressor, an inlet port being in communication with the interior of a cam ring is provided on a side-block which covers one end of the cam ring. The position of the opening is moved along a cam surface so that due to the rotation of the vanes the compression starting position is changed.
Such variable-delivery vane-type rotary compressors are described in the Japanese Patent First Publication (Jikkai) Showa No. 59-76786 and the Japanese Patent First Publication (Tokkai) Showa No. 60-259789. The former is provided with a control disc between the cam ring and the side-block. The control disc is provided with a circular inlet port opposing an actuating chamber. The control disc rotates about the axis of a rotor so that the position of the inlet port can be changed. On the other hand, the latter has a cam ring provided with an inlet port, the end opening of which is provided on the inside surface. In addition one end of the cam ring is provided with a side-block. A arc-shaped inlet port, which extends beside the cam surface, is formed on the side-block. A slide control member is slidably inserted into the inlet port of the side-block. By moving the position of the control member, compression starting position of the vane can be changed.
However, in these conventional variable-delivery vane-type rotary compressors, aperture area of the inlet port can not be enlarged. Therefore, when discharge is controlled by changing the position of the inlet port and delaying the compression starting position of the vane, negative pressure occurs in rear of the vane until the vane reaches the inlet starting point. Therefore, there is a disadvantage in that power loss is increased due to the pressure differential between the front and rear of the vane.
On the other hand, when the side-block is provided with an inlet port and a slide control member other than the inlet port provided on the cam ring, there is no power loss. However, since the inlet port can not be formed in all of the actuating chambers, the variable range of discharge is small (for example, about 50 to 100%). Therefore, there is a disadvantage in that good driving condition can not be achieved since ON-OFF of the clutch due to supercooling of the air conditioner during high-speed operation of the engine or ON-OFF of the clutch when low-load is applied to the air conditioner can not be prevented.